Growth processes in teeth distinguish modern humans from Homo erectus and earlier hominins.

A modern human-like sequence of dental development, as a proxy for the pace of life history, is regarded as one of the diagnostic hallmarks of our own genus Homo. Brain size, age at first reproduction, lifespan and other life-history traits correlate tightly with dental development. Here we report differences in enamel growth that show the earliest fossils attributed to Homo do not resemble modern humans in their development. We used daily incremental markings in enamel to calculate rates of enamel formation in 13 fossil hominins and identified differences in this key determinant of tooth formation time. Neither australopiths nor fossils currently attributed to early Homo shared the slow trajectory of enamel growth typical of modern humans; rather, both resembled modern and fossil African apes. We then reconstructed tooth formation times in australopiths, in the approximately 1.5-Myr-old Homo erectus skeleton from Nariokotome, Kenya, and in another Homo erectus specimen, Sangiran S7-37 from Java. These times were shorter than those in modern humans. It therefore seems likely that truly modern dental development emerged relatively late in human evolution.     

Neanderthal cranial ontogeny and its implications for late hominid diversity

Homo neanderthalensis has a unique combination of craniofacial features that are distinct from fossil and extant 'anatomically modern' Homo sapiens (modern humans). Morphological evidence, direct isotopic dates and fossil mitochondrial DNA from three Neanderthals indicate that the Neanderthals were a separate evolutionary lineage for at least 500,000 yr. However, it is unknown when and how Neanderthal craniofacial autapomorphies (unique, derived characters) emerged during ontogeny. Here we use computerized fossil reconstruction and geometric morphometrics to show that characteristic differences in cranial and mandibular shape between Neanderthals and modern humans arose very early during development, possibly prenatally, and were maintained throughout postnatal ontogeny. Postnatal differences in cranial ontogeny between the two taxa are characterized primarily by heterochronic modifications of a common spatial pattern of development. Evidence for early ontogenetic divergence together with evolutionary stasis of taxon-specific patterns of ontogeny is consistent with separation of Neanderthals and modern humans at the species level.     

The Homo sapiens Cave hominin site of Mulan Mountain, Jiangzhou District, Chongzuo, Guangxi with emphasis on its age

One of the most hotly debated and frontal issues in paleoanthropology focuses on the origins of modern humans. Recently, an incomplete hominin mandible with a distinctly weaker mental protuberance than modern human and a great variety of coexisting fossil mammals were unearthed from the Homo sapiens Cave of Mulan Mountain, Chongzuo, Guangxi. The mammalian fauna from the Homo sapiens Cave characterized by the combination of Elephas kiangnanensis, first occurring Elephas maixmus, and Megatapirus augustus, and strikingly different from the Early Pleistocene Gigantopithecus fauna and the Middle Pleistocene Ailuropoda-Stogodon fauna of South China could be regarded as an early representive of the typical Asian elephant fauna. Faunal analysis, biostratigraphic correlation, and, most importantly, U-series dating all consistently support an estimate of ca. 110 ka for the age of the fossil Homo sapiens and coexisting mammalian fauna, that is, the early Late Pleistocene. The fauna is mainly made up of tropical-subtropical elements, but grassland elements have a much greater variety than forest elements, which probably indicates a drier climate at that time. This discovery of early Homo sapiens at the Mulan Mountain will play a significant role in the study of the origin and its environmental background of modern humans.     

First fossil chimpanzee

There are thousands of fossils of hominins, but no fossil chimpanzee has yet been reported. The chimpanzee (Pan) is the closest living relative to humans. Chimpanzee populations today are confined to wooded West and central Africa, whereas most hominin fossil sites occur in the semi-arid East African Rift Valley. This situation has fuelled speculation regarding causes for the divergence of the human and chimpanzee lineages five to eight million years ago. Some investigators have invoked a shift from wooded to savannah vegetation in East Africa, driven by climate change, to explain the apparent separation between chimpanzee and human ancestral populations and the origin of the unique hominin locomotor adaptation, bipedalism. The Rift Valley itself functions as an obstacle to chimpanzee occupation in some scenarios. Here we report the first fossil chimpanzee. These fossils, from the Kapthurin Formation, Kenya, show that representatives of Pan were present in the East African Rift Valley during the Middle Pleistocene, where they were contemporary with an extinct species of Homo. Habitats suitable for both hominins and chimpanzees were clearly present there during this period, and the Rift Valley did not present an impenetrable barrier to chimpanzee occupation.     

Early brain growth in Homo erectus and implications for cognitive ability

Humans differ from other primates in their significantly lengthened growth period. The persistence of a fetal pattern of brain growth after birth is another important feature of human development. Here we present the results of an analysis of the 1.8-million-year-old Mojokerto child (Perning 1, Java), the only well preserved skull of a Homo erectus infant, by computed tomography. Comparison with a large series of extant humans and chimpanzees indicates that this individual was about 1 yr (0-1.5 yr) old at death and had an endocranial capacity at 72-84% of an average adult H. erectus. This pattern of relative brain growth resembles that of living apes, but differs from that seen in extant humans. It implies that major differences in the development of cognitive capabilities existed between H. erectus and anatomically modern humans.     

New fossils from Koobi Fora in northern Kenya confirm taxonomic diversity in early Homo

Since its discovery in 1972 (ref. 1), the cranium KNM-ER 1470 has been at the centre of the debate over the number of species of early Homo present in the early Pleistocene epoch of eastern Africa. KNM-ER 1470 stands out among other specimens attributed to early Homo because of its larger size, and its flat and subnasally orthognathic face with anteriorly placed maxillary zygomatic roots. This singular morphology and the incomplete preservation of the fossil have led to different views as to whether KNM-ER 1470 can be accommodated within a single species of early Homo that is highly variable because of sexual, geographical and temporal factors, or whether it provides evidence of species diversity marked by differences in cranial size and facial or masticatory adaptation. Here we report on three newly discovered fossils, aged between 1.78 and 1.95 million years (Myr) old, that clarify the anatomy and taxonomic status of KNM-ER 1470. KNM-ER 62000, a well-preserved face of a late juvenile hominin, closely resembles KNM-ER 1470 but is notably smaller. It preserves previously unknown morphology, including moderately sized, mesiodistally long postcanine teeth. The nearly complete mandible KNM-ER 60000 and mandibular fragment KNM-ER 62003 have a dental arcade that is short anteroposteriorly and flat across the front, with small incisors; these features are consistent with the arcade morphology of KNM-ER 1470 and KNM-ER 62000. The new fossils confirm the presence of two contemporary species of early Homo, in addition to Homo erectus, in the early Pleistocene of eastern Africa.     

Anthropology: the earliest toothless hominin skull

The site of Dmanisi in the Eurasian republic of Georgia has yielded striking hominin, faunal and archaeological material as evidence for the presence of early Homo outside Africa 1.77 million years ago, documenting an important episode in human evolution. Here we describe a beautifully preserved skull and jawbone from a Dmanisi hominin of this period who had lost all but one tooth several years before death. This specimen not only represents the earliest case of severe masticatory impairment in the hominin fossil record to be discovered so far, but also raises questions about alternative subsistence strategies in early Homo.     

The brain morphology of Homo Liujiang cranium fossil by three-dimensional computed tomography

The Liujiang cranium is the most complete and well-preserved late Pleistocene human fossils ever unearthed in south China. Because the endocranial cavity is filled with hard stone matrix, earlier studies focused only on the exterior morphology of the specimen using the traditional methods. In order to derive more information for the phyletic evaluation of the Liujiang cranium, high-resolution industrial computed tomography （CT） was used to scan the fossil, and the three-dimensional （3D） brain image was reconstructed. Compared with the endocasts of the hominin fossils （Hexian, Zhoukoudian, KNM-WT 15000, Sm 3, Kabwe, Brunn 3, Predmost） and modern Chinese, most morphological features of the Liujiang brain are in common with modern humans, including a round brain shape, bulged and wide frontal lobes, an enlarged brain height, a full orbital margin and long parietal lobes. A few differences exist between Liujiang and the modern Chinese in our sample, including a strong posterior projection of the occipital lobes, and a reduced cerebellar lobe. The measurement of the virtual endocast shows that the endocranial capacity of Liujiang is 1567 cc, which is in the range of Late Homo sapiens and much beyond the mean of modern humans. The brain morphology of Liujiang is assigned to Late Homo sapiens.     

Patterns and rates of enamel growth in the molar teeth of early hominids

A recent study of the surface manifestation of incremental lines associated with enamel formation suggested that the crowns of early hominid incisor teeth were formed more rapidly than those of modern humans. In the absence of comparative data, the authors were forced to assume that enamel increments in fossil teeth were similar to those in modern humans. We have used evidence from the fractured surfaces of molar teeth to deduce estimates for both long- and short-period incremental growth markers within enamel in east African 'robust' australopithecine and early Homo teeth. We conclude that in these early hominids, crown formation times in posterior teeth, particularly in the large thick enamelled molar teeth of the east African 'robust' australopithecines, were shorter than those of modern humans. This evidence, considered together with data on crown and root formation times in modern apes, suggests that the posterior teeth in these hominids both formed and erupted more rapidly than those of modern man. These results have implications for attempts to assess dental and skeletal maturity in hominids.     

Pleistocene Homo sapiens from Middle Awash,Ethiopia

The origin of anatomically modern Homo sapiens and the fate of Neanderthals have been fundamental questions in human evolutionary studies for over a century. A key barrier to the resolution of these questions has been the lack of substantial and accurately dated African hominid fossils from between 100,000 and 300,000 years ago. Here we describe fossilized hominid crania from Herto, Middle Awash, Ethiopia, that fill this gap and provide crucial evidence on the location, timing and contextual circumstances of the emergence of Homo sapiens. Radioisotopically dated to between 160,000 and 154,000 years ago, these new fossils predate classic Neanderthals and lack their derived features. The Herto hominids are morphologically and chronologically intermediate between archaic African fossils and later anatomically modern Late Pleistocene humans. They therefore represent the probable immediate ancestors of anatomically modern humans. Their anatomy and antiquity constitute strong evidence of modern-human emergence in Africa.     

Stratigraphic,chronological and behavioural contexts of Pleistocene Homo sapiens from Middle Awash,Ethiopia

Clarifying the geographic, environmental and behavioural contexts in which the emergence of anatomically modern Homo sapiens occurred has proved difficult, particularly because Africa lacked adequate geochronological, palaeontological and archaeological evidence. The discovery of anatomically modern Homo sapiens fossils at Herto, Ethiopia, changes this. Here we report on stratigraphically associated Late Middle Pleistocene artefacts and fossils from fluvial and lake margin sandstones of the Upper Herto Member of the Bouri Formation, Middle Awash, Afar Rift, Ethiopia. The fossils and artefacts are dated between 160,000 and 154,000 years ago by precise age determinations using the 40Ar/39Ar method. The archaeological assemblages contain elements of both Acheulean and Middle Stone Age technocomplexes. Associated faunal remains indicate repeated, systematic butchery of hippopotamus carcasses. Contemporary adult and juvenile Homo sapiens fossil crania manifest bone modifications indicative of deliberate mortuary practices.     

Identification of Zhoukoudian <Emphasis Type="Italic">Homo erectus</Emphasis> brain asymmetry using 3D laser scanning

Endocasts are important materials used for the study of human brain evolution, and allow examination of the external features of brain anatomy from the inside the cranium. Studies examining brain asymmetries in fossil hominids are usually limited to scoring of differences in hemisphere protrusion rostrally and caudally, or to comparing the width of the hemispheres. In the present study, using 3D laser scanning, we examined asymmetries of the hemisphere volumes and surface areas in the Zhoukoudain (ZKD) Homo erectus, dated to 0.4–0.8 Ma. Compared with modern endocasts, we found that the absolute hemisphere volumes and surface areas exhibited no significant asymmetries in the ZKD or in modern specimens. However, the relative hemisphere volumes against surface areas differed between the two groups. When comparing the relative sizes between the left and right hemispheres, the ZKD specimens exhibited a greater variation than in the modern humans; there were no differences in the two hemispheres in the ZKD specimens, while in the modern endocasts the left hemisphere was significantly greater than the right hemisphere. These data suggest that brain asymmetries originated from relative brain sizes rather than absolute brain volumes during human evolution. These anatomical changes are likely related to the origin of human brain lateralization.     

Analysis of one million base pairs of Neanderthal DNA

Neanderthals are the extinct hominid group most closely related to contemporary humans, so their genome offers a unique opportunity to identify genetic changes specific to anatomically fully modern humans. We have identified a 38,000-year-old Neanderthal fossil that is exceptionally free of contamination from modern human DNA. Direct high-throughput sequencing of a DNA extract from this fossil has thus far yielded over one million base pairs of hominoid nuclear DNA sequences. Comparison with the human and chimpanzee genomes reveals that modern human and Neanderthal DNA sequences diverged on average about 500,000 years ago. Existing technology and fossil resources are now sufficient to initiate a Neanderthal genome-sequencing effort.     

Surprisingly rapid growth in Neanderthals

Life-history traits correlate closely with dental growth, so differences in dental growth within Homo can enable us to determine how somatic development has evolved and to identify developmental shifts that warrant species-level distinctions. Dental growth can be determined from the speed of enamel formation (or extension rate). We analysed the enamel extension rate in Homo antecessor (8 teeth analysed), Homo heidelbergensis (106), Homo neanderthalensis ('Neanderthals'; 146) and Upper Palaeolithic-Mesolithic Homo sapiens (100). Here we report that Upper Palaeolithic-Mesolithic H. sapiens shared an identical dental development pattern with modern humans, but that H. antecessor and H. heidelbergensis had shorter periods of dental growth. Surprisingly, Neanderthals were characterized by having the shortest period of dental growth. Because dental growth is an excellent indicator of somatic development, our results suggest that Neanderthals developed faster even than their immediate ancestor, H. heidelbergensis. Dental growth became longer and brain size increased from the Plio-Pleistocene in hominid evolution. Neanderthals, despite having a large brain, were characterized by a short period of development. This autapomorphy in growth is an evolutionary reversal, and points strongly to a specific distinction between H. sapiens and H. neanderthalensis.     

Genetics and the making of Homo sapiens

Understanding the genetic basis of the physical and behavioural traits that distinguish humans from other primates presents one of the great new challenges in biology. Of the millions of base-pair differences between humans and chimpanzees, which particular changes contributed to the evolution of human features after the separation of the Pan and Homo lineages 5-7 million years ago? How can we identify the 'smoking guns' of human genetic evolution from neutral ticks of the molecular evolutionary clock? The magnitude and rate of morphological evolution in hominids suggests that many independent and incremental developmental changes have occurred that, on the basis of recent findings in model animals, are expected to be polygenic and regulatory in nature. Comparative genomics, population genetics, gene-expression analyses and medical genetics have begun to make complementary inroads into the complex genetic architecture of human evolution.     

Late Miocene hominids from the Middle Awash, Ethiopia.

Molecular studies suggest that the lineages leading to humans and chimpanzees diverged approximately 6.5-5.5 million years (Myr) ago, in the Late Miocene. Hominid fossils from this interval, however, are fragmentary and of uncertain phylogenetic status, age, or both. Here I report new hominid specimens from the Middle Awash area of Ethiopia that date to 5.2-5.8 Myr and are associated with a wooded palaeoenvironment. These Late Miocene fossils are assigned to the hominid genus Ardipithecus and represent the earliest definitive evidence of the hominid clade. Derived dental characters are shared exclusively with all younger hominids. This indicates that the fossils probably represent a hominid taxon that postdated the divergence of lineages leading to modern chimpanzees and humans. However, the persistence of primitive dental and postcranial characters in these new fossils indicates that Ardipithecus was phylogenetically close to the common ancestor of chimpanzees and humans. These new findings raise additional questions about the claimed hominid status of Orrorin tugenensis, recently described from Kenya and dated to approximately 6 Myr.     

Independent evolution of bitter-taste sensitivity in humans and chimpanzees

It was reported over 65 years ago that chimpanzees, like humans, vary in taste sensitivity to the bitter compound phenylthiocarbamide (PTC). This was suggested to be the result of a shared balanced polymorphism, defining the first, and now classic, example of the effects of balancing selection in great apes. In humans, variable PTC sensitivity is largely controlled by the segregation of two common alleles at the TAS2R38 locus, which encode receptor variants with different ligand affinities. Here we show that PTC taste sensitivity in chimpanzees is also controlled by two common alleles of TAS2R38; however, neither of these alleles is shared with humans. Instead, a mutation of the initiation codon results in the use of an alternative downstream start codon and production of a truncated receptor variant that fails to respond to PTC in vitro. Association testing of PTC sensitivity in a cohort of captive chimpanzees confirmed that chimpanzee TAS2R38 genotype accurately predicts taster status in vivo. Therefore, although Fisher et al.'s observations were accurate, their explanation was wrong. Humans and chimpanzees share variable taste sensitivity to bitter compounds mediated by PTC receptor variants, but the molecular basis of this variation has arisen twice, independently, in the two species.     

Endurance running and the evolution of Homo

Striding bipedalism is a key derived behaviour of hominids that possibly originated soon after the divergence of the chimpanzee and human lineages. Although bipedal gaits include walking and running, running is generally considered to have played no major role in human evolution because humans, like apes, are poor sprinters compared to most quadrupeds. Here we assess how well humans perform at sustained long-distance running, and review the physiological and anatomical bases of endurance running capabilities in humans and other mammals. Judged by several criteria, humans perform remarkably well at endurance running, thanks to a diverse array of features, many of which leave traces in the skeleton. The fossil evidence of these features suggests that endurance running is a derived capability of the genus Homo, originating about 2 million years ago, and may have been instrumental in the evolution of the human body form.     

Earliest Homo.

The origin of our own genus, Homo, has been tentatively correlated with worldwide climatic cooling documented at about 2.4 Myr (million years). It has also been conjectured that members of Homo made the first stone tools, currently dated at 2.6-2.4 Myr. But fossil specimens clearly attributable to Homo before about 1.9 Myr have been lacking. In 1967 a fossil hominoid temporal bone (KNM-BC1) from the Chemeron Formation of Kenya was described as family Hominidae gen. et sp. indet. Although a surface find, its provenance within site JM85 (BPRP site K002) was established and a stratigraphic section provided indicating the specimen's position. This evidence has been affirmed but the exact age of the fossil was never determined, and the absence of suitable comparative hominid material has precluded a more definitive taxonomic assignment. Here we present 40Ar/39Ar age determinations on material from the hominid site indicating an age of 2.4 Myr. In addition, comparative studies allow us to assign KNM-BC1 to the genus Homo, making it the earliest securely known fossil of our own genus found so far.     

Early stone technology on Flores and its implications for Homo floresiensis

In the Soa Basin of central Flores, eastern Indonesia, stratified archaeological sites, including Mata Menge, Boa Lesa and Kobatuwa (Fig. 1), contain stone artefacts associated with the fossilized remains of Stegodon florensis, Komodo dragon, rat and various other taxa. These sites have been dated to 840-700 kyr bp (thousand years before present). The authenticity of the Soa Basin artefacts and their provenance have been demonstrated by previous work, but to quell lingering doubts, here we describe the context, attributes and production modes of 507 artefacts excavated at Mata Menge. We also note specific similarities, and apparent technological continuity, between the Mata Menge stone artefacts and those excavated from Late Pleistocene levels at Liang Bua cave, 50 km to the west. The latter artefacts, dated to between 95-74 and 12 kyr ago, are associated with the remains of a dwarfed descendent of S. florensis, Komodo dragon, rat and a small-bodied hominin species, Homo floresiensis, which had a brain size of about 400 cubic centimetres. The Mata Menge evidence negates claims that stone artefacts associated with H. floresiensis are so complex that they must have been made by modern humans (Homo sapiens).